Abstract：
Succinate dehydrogenase inhibitors (SDHIs) as one of the fastest-growing fungicide categories for plant protection. In this study, a series of N\'-phenyl pyridylcarbohydrazides as analogues of commercial SDHIs were designed and evaluated for inhibition activity on phytopathogenic fungi to search for potential novel SDHIs. The determination of antifungal activity in vitro and in vivo led to the discovery of a series of compounds with high activity and broad-spectrum property. Especially, N\'-(4-fluorophenyl)picolinohydrazide (1c) and N\'-(3,4-fluorophenyl)picolinohydrazide (1ae) showed 0.041-1.851 μg/mL of EC50 values on twelve fungi, superior to positive controls carbendazim and boscalid. In vivo activity, 1c at 50 μg/mL showed 61% of control efficacy at the post-treatment 9th day for the infection of P. piricola on apples, slightly smaller than 70% of carbendazim. In terms of action mechanism, 1c showed strong inhibition activity with IC50 of 0.107 μg/mL on SDH in Alternaria brassicae, superior to positive SDHI boscalid (IC50 0.182 μg/mL). Molecular docking indicated that 1c can well bind with the ubiquinone-binding region of SDH mainly by hydrogen bond, carbon hydrogen bond, π-alkyl, amide-π stacking, F-N and F-H interactions. Furthermore, scanning and transmission electron micrographs showed that 1c was able to obviously change the structure of mycelia and cell membrane. Fluorescence staining analysis showed that 1c could increase both the intracellular reactive oxygen species level and mitochondrial membrane potential. Finally, seed germination test, seedling growth test and cytotoxicity assay showed that 1c had very low toxicity to plant growth and mammalian cells. Thus, N\'-phenyl pyridylcarbohydrazides especially 1c and 1ae can be considered promising fungicide alternatives for plant protection.
摘要：
琥珀酸脱氢酶抑制剂（SDHI）是植物保护中增长最快的杀菌剂类别之一。在这项研究中,设计了一系列N'-苯基吡啶基碳酰肼作为商业SDHI的类似物，并评估了其对植物病原真菌的抑制活性，以寻找潜在的新型SDHI。体外和体内抗真菌活性的测定导致发现了一系列具有高活性和广谱特性的化合物。尤其是,N'-（4-氟苯基）吡啶酰肼（1c）和N'-（3,4-氟苯基）吡啶酰肼（1ae）在十二种真菌上显示0.041-1.851μg/mL的EC50值，优于阳性对照多菌灵和啶酰菌胺。体内活性,1c在50μg/mL时，在治疗后第9天，对苹果上的P.piricola感染显示出61％的对照功效，略小于70%的多菌灵。在行动机制方面,1c显示出强抑制活性，IC50为0.107μg/mL，优于阳性SDHI啶菌液（IC500.182μg/mL）。分子对接表明1c主要通过氢键与SDH的泛醌结合区结合良好,碳氢键，π-烷基，酰胺-π堆叠，F-N和F-H相互作用。此外，扫描电镜和透射电镜显示1c能明显改变菌丝和细胞膜的结构。荧光染色分析表明，1c可以提高细胞内活性氧水平和线粒体膜电位。最后,种子发芽试验,幼苗生长试验和细胞毒性试验表明，1c对植物生长和哺乳动物细胞的毒性非常低。因此，N'-苯基吡啶基碳酰肼，尤其是1c和1ae，可以被认为是植物保护的有前途的杀真菌剂替代品。
